The present invention relates generally to systems for controlling semiautomatic transmissions, and more specifically to systems for switching between manual and automatic control modes of a number of top gears of a semiautomatic transmission.
Semiautomatic transmissions, which are defined for purposes of the present invention as transmissions having a number of manually selectable gear ratios and a number of automatically selectable gear ratios, are known and widely used, particularly in the heavy duty truck industry. In vehicles including such transmissions, a control computer is typically provided for controlling the shifting between the automatically selectable gear ratios in accordance with various engine and vehicle operating conditions.
One specific embodiment of the foregoing class of transmissions is commonly referred to as a xe2x80x9cTOP-2xe2x80x9d transmission, wherein a number of the numerically higher gear ratios (i.e. numerically lower gears such as 1st, 2nd, 3rd, etc.) are manually selectable, and shifting between the numerically lowest two gear ratios (i.e. numerically highest gears or Top-2 gears) is managed by a control computer pursuant to a gear shifting control algorithm. Examples of such Top-2 type transmissions and control algorithms therefore are given in U.S. Pat. Nos. 5,393,276, 5,393,277, 5,401,223, 5,498,195, 5,591,102, 5,609,548 and 5,638,271 to White et al., each of which are assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference.
While the foregoing Top-2 type transmissions and controls therefore have been well received in the heavy duty truck industry, they have a number of drawbacks associated with the operation thereof. For example, some drivers of such vehicles perceive the automatic control of the Top-2 gears as dangerous under certain operating conditions such as when traveling on slippery roads. Accordingly, what is needed is a system for allowing driver selectability of Top-2 or non-Top-2 operation, i.e. switchability between manual and automatic control of the Top-2 gears, or at least a system for allowing a fleet owner/manager to enable/disable automatic control of the Top-2 gears via a service tool not available to the driver. Under conditions wherein shifting between the Top-2 gears is not automatically controlled via a control computer pursuant to a Top-2 control algorithm, but is rather manually controlled by the driver in accordance with known techniques, it would further be preferable to institute control over the maximum steady state vehicle or engine speeds during Top-2 gear operation.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for selecting between automatic and manual control of a number of gear ratios of a semiautomatic transmission comprises an internal combustion engine coupled to a semiautomatic transmission having a number of manually selectable gear ratios and a number of automatically selectable gear ratios, means for determining an engine fueling rate, a switch having a first switch position and a second switch position, a memory unit including a software algorithm for controlling shifting between the number of automatically selectable gear ratios, and a control computer. The control computer is responsive to the first switch position to execute the software algorithm and thereby control shifting between the automatically selectable gear ratios, and is responsive to the second switch position to inhibit execution of the software algorithm if the engine is currently engaged with one of the number of automatically selectable gear ratios and the fueling rate is less than a threshold fueling rate.
In accordance with another aspect of the present invention, a system for selecting between automatic and manual control of a number of gear ratios of a semiautomatic transmission comprises an internal combustion engine coupled to a semiautomatic transmission having a number of manually selectable gear ratios and a number of automatically selectable gear ratios, means for determining engine load, means for determining one of engine speed and vehicle road speed, a memory unit including a software algorithm for controlling shifting between the number of automatically selectable gear ratios, and a control computer. The control computer is operable in a first mode to execute the software algorithm and thereby control shifting between the number of automatically selectable gear ratios, and in a second mode to inhibit execution of the software algorithm such that the number of automatically selectable gear ratios are manually selectable. The control computer is further operable in the second mode to determine a currently selected gear ratio of the transmission and reduce one of an engine speed limit and vehicle speed limit if a numerically lowest one of the selectable gear ratios is not currently selected and the engine load is below an engine load threshold, and to further reduce one of engine speed and vehicle speed if the one of engine speed and vehicle speed is above a corresponding one of the engine speed and vehicle speed limit.
One object of the present invention is to provide a system for selecting between automatic and manual control of a number of gear ratios of a semiautomatic transmission.
Another object of the present invention is to provide such a system wherein a gear down protection algorithm is instituted whenever control of the number of gear ratios of the semiautomatic transmission is switched to manual control thereof.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.